1. Field of the Invention
The present invention relates to an illuminating mechanism of a rotary electric component capable of illuminating a display portion of a faceplate disposed around a rotary knob, and specifically to an illuminating mechanism which can be suitably applied to automotive rotary electric components such as an air conditioning system, an audio system, and the like.
2. Description of the Related Art
In rotary electric components used in an automotive air conditioning system, an automotive audio system, and the like, in order for an occupant to see the position of a rotary knob in a dark place, an illuminating mechanism, in which a faceplate having a display portion formed around the rotary knob is disposed and the display portion can be illuminated from the rear surface of the faceplate, is widely employed (for example, see Patent Document 1).
FIG. 6 is a cross-sectional view illustrating an example of a conventional automotive rotary electric component employing this kind of illuminating mechanism. The rotary electric component 1 shown in FIG. 6 comprises a cylindrical rotary knob 2, a rotary encoder of which a rotor portion 6 is rotated by the rotary knob 2, an annular thin faceplate 3 disposed around the rotary knob 2, a holder 4 for bonding and fixing an inner circumferential portion and an outer circumferential portion of the rear surface of the faceplate 3, a light guiding member 5 which is held by the holder 4 and of which an inner ring portion 5a and an outer ring portion 5b are connected to each other, a light source 7 disposed adjacent to the light guiding member 5, and a circuit board 8 on which the rotary encoder, the light source 7, and so on are mounted.
The rotary knob 2 is made of a synthetic resin material having a light shielding property, and a positional mark 2a to be illuminated through the inner ring portion 5a of the light guiding member 5 is attached to a part of the rotary knob 2. The faceplate 3 is formed by applying a light shielding paint to the front surface of a light-transmitting resin plate except for a display portion 3a and attaching a colored toning sheet to the entire rear surface of the resin plate, and the display portion 3a is illuminated with the desired color corresponding to the toning sheet through the outer ring portion 5b of the light guiding member 5. The display portion 3a is an illuminating area in which symbols or letters, etc. as indexes of the position of the rotary knob 2 are displayed, and by seeing which place the positional mark 2a indicates, an occupant can confirm the position of the rotary knob 2. The light guiding member 5 is formed by molding a material having a sufficient light-transmitting property such as acryl resin. The light incident on an end surface 5c of the light guiding member 5 from the light source 7 is emitted from the inner ring portion 5a to the rotary knob 2 and is also emitted from the outer ring portion 5b to the faceplate 3. The holder 4, which is formed by molding resin, is also used as an upper case formed as one body together with a lower case (not shown). Furthermore, respective front end surfaces of a small-diameter annular portion 4a and a large-diameter annular portion 4b of the holder 4 are bonded and fixed to the faceplate 3, and the inner ring portion 5a and the outer ring portion 5b of the light guiding member 5 are arranged to sandwich the small-diameter annular portion 4a. The circuit board 8 is attached to the lower case, and the rotary electric component 1 is electrically connected to an external circuit through a connector (not shown) provided on the circuit board 8 or the lower case.
Furthermore, since the rotary knob 2 is freely rotatable with respect to the holder 4, a gap is required between the small-diameter annular portion 4a of the holder 4 and the rotary knob 2. However, since the gap tends to form an optical path through which the light emitted from the inner ring portion 5a leaks, light leakage may be caused, thereby compromising the design of the illuminating system. Therefore, a flange portion 2b is usually provided to protrude from the rotary knob 2, and the flange portion 2b overlaps the small-diameter annular portion 4a of the holder 4.
The rotary electric component 1 described above is assembled in a circular cutout 11 formed in a front panel 10 of a vehicle cabin with the display portion 3a of the faceplate 3 and the rotary knob 2 exposed, and the rotary knob 2 protrudes from the cutout 11. When an occupant manipulates the rotary knob 2, the occupant can confirm the position of rotary knob 2 by seeing a relative position between the positional mark 2a and the display portion 3a. In addition, since the positional mark 2a and the display portion 3a are illuminated from the rear surface thereof, the occupant can manipulate the rotary knob 2 without difficulty even in darkness such as might be experienced during nighttime driving.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 7-335076 (pp. 2 to 4, FIG. 4)
In the conventional automotive rotary electric component 1 as described above, in order to prevent the light from the inner ring portion 5a for illuminating the positional mark 2a from leaking forward, the flange portion 2b protrudes from the rotary knob 2. However, since an inner circumferential portion and an outer circumferential portion of the faceplate 3 are bonded and fixed to the holder 4, the light from the outer ring portion 5b for illuminating the display portion 3a does not leak forward, so that a specific countermeasure against the light leakage thereof is not considered. However, since a vehicle cabin may reach extremely high temperatures and its temperature variation is large, adhesive strength may deteriorate over long periods of time, so that a part of the faceplate 3 may get loose from the holder 4. Of course, as shown in FIG. 6, the looseness of the outer circumferential portion of the faceplate 3 can be prevented by employing a construction in which the faceplate 3 is interposed between the front panel 10 and the holder 4. However, there is no solution of light leakage when the inner circumferential portion gets loose.
That is, if a part of the inner circumferential portion of the faceplate 3 gets loose from the holder 4 resulting in a gap, as indicated by arrow B in FIG. 6, the light from the outer ring portion 5b for illuminating the display portion 3a passes through the gap and leaks around the rotary knob 2, thereby compromising the design of the illuminating system markedly. Furthermore, since the display portion 3a should be exposed from the opening portion 11, a construction in which the inner circumferential portion of the faceplate 3 is interposed between the front panel 10 and the holder 4 cannot be employed.